As someone who has tended to avoid organised holidays, I was astonished by the tally racked up by my fellow travellers on a tour to Genoa and Turin. Rita was on her 37th tour and was clearly ready for more. A spry, retired teacher from Wales, with a self-deprecating sense of humour, she had looked at cheaper options but concluded that Martin Randall offered best value for money.

Andrew and Hilary, a married couple, were on their 19th tour. A fourth member, Margaret, had come along, despite not being interested in the Baroque art that featured prominently on the programme. There was evidently something special about travelling with Martin Randall. I was curious to find out what it was.

First, the itinerary. Genoa and Turin worked as a combination because they are so different. Formerly a great maritime republic, Genoa is squeezed between the mountains and the sea. It has a flourishing port, Renaissance and Baroque palaces with stupendous façades that were declared a world heritage site by Unesco in 2006, and a skyline that climbs dramatically from the waterfront.

Turin, by contrast, lies on a plateau by the River Po and spreads itself majestically through a network of avenues and squares laid out in the 17th and 18th centuries after the royal House of Savoy had moved there from Chambéry. The presence of Fiat makes it one of the main manufacturing centres of Italy. And the sobriety of its architecture reminds one of northern Europe.

Our guide was Dr Luca Leoncini, a youthful-looking 50 year-old who for the past 18 years has been director of the Palazzo Reale, the grandest of the Genoese palaces. As expected, he was erudite. But more important was his enthusiasm.

He loves what he calls "my palace" and regrets that the House of Savoy removed 40 of its works of art to Turin in the 19th century, one of which, he noted, was being used as a fire screen. More recently, a gilded clock from the Palazzo Reale was commandeered by Silvio Berlusconi and returned only after a public outcry. Luca made it abundantly clear that he was not one of the prime minister's fans.

In the Palazzo Rosso in Genoa, he brought two paintings to life for us by quoting what his teacher had said about them. A Guercino of the death of Cleopatra, the cream nude surrounded by a purple drape, showed that "abandonment to love and death can look alike", while the clothes in a Bernardo Strozzi portrait of a cook were "white like the foam of the sea".

In Turin, rather than dragging us right around the royal collection, he simply showed us the paintings he liked and then left us to our own devices. Margaret, my travelling companion with an aversion to the Baroque, went in search of a work by the 15th-century Flemish artist Rogier van der Weyden, only to find that the room that housed it was closed. That sort of disappointment is not uncommon in Italy: in Turin the cathedral was shut because they were dismantling the structures for an exhibition of the Holy Shroud that had just ended.

Members of our group, middle-aged and elderly, came from Australia and the United States as well as Britain. There were three married couples and exactly the same number of men as of women. Widely travelled and well versed in Italian art, they made for stimulating company.

Each day we would set off at the reasonable hour of nine; Luca, an elegant, darkly clad figure moving with deceptive speed ahead of us. In Genoa much of our time was spent in the palaces along the Via Balbi and the Via Garibaldi, fruit of the fabulous wealth acquired by what was successively a trading power and banking centre of European importance.

But the city also has an extensive medieval core centred on the cathedral of San Lorenzo. The west end is a wonderful, striped confection of variegated marble in the centre of which the martyr to whom the building is dedicated lies on his gridiron gazing at Christ in majesty above, while squat little figures ply the bellows.

The striped effect is repeated in the Piazza San Matteo on the façades of lofty houses with Gothic arcading. In the church that gives its name to the square, Andrea Doria, the great Renaissance sailor-statesman, is buried. We crowded into a little crypt to look at the simple slab that marks his grave.

The admiral's old palazzo is on the western edge of town in what would have then been countryside. His fleet of six ships would have been moored at the end of the garden. Now the property is abutted by a hideous flyover, dating from the Sixties, which runs around the perimeter of the port.

Inside the villa, we were tremendously taken by the tapestries. There is a series on the Battle of Lepanto, the famous victory over the Turks in 1571 in which Doria played a prominent part.

If that is historically fascinating, scenes from the Legend of Alexander the Great, woven in the mid-15th century, are simply fantastic. He is portrayed exploring the heavens in a kind of spaceship raised aloft by griffins, then the depths of the sea in a glass barrel held under water by courtiers with oars.

We saw a daunting number of paintings during our week together. Two in Genoa took our fancy in very different ways.

The first, in the church of San Siro, was Orazio Gentileschi's Annunciation, a work of transcendent beauty, from the grace of the figures to the colours of the drapery and the mysterious light that emanates from outside the frame.

The second, if you can imagine it, is a theological statement that made us chuckle. The Virgin has crushed a dragon into a two- dimensional mat. A putto is biffing it with the butt of a cross but an apelike arm still hangs down, offering an apple to Adam and Eve, who crouch, terrified, in a corner. It was painted by the Genoese Domenico Piola for the church of Santissima Annunziata del Vastato.

With such artistic wealth, there is a danger of surfeit. I asked Luca about this. He agreed that our programme was heavily loaded but said that he saw his job as introducing us to as wide a range of works as possible. Mercifully, he understood how much Baroque detail we could take at one go.

The itinerary allowed space for us to go off on our own. On Luca's recommendation, I visited the Staglieno cemetery on the northern edge of Genoa. I have never seen such an astonishing collection of funerary sculpture, testimony to the wealth, and artistic pretensions, of the Genoese bourgeoisie in the 19th and early 20th centuries.

Among the subjects were a mourning family gathered around a recumbent paterfamilias; a seated young woman bent forward in grief, her hair falling to her feet; a gloomy widow sitting at the foot of a wooden door with iron clasps through which her husband had metaphorically passed; and a woman with a distinctly dusty chest struggling to free herself from the grasp of a veiled skeleton.

In Turin the dominant figure on our itinerary was the Sicilian architect Filippo Juvarra, who was employed by King Vittorio Amedeo II between 1714 and 1735. It took me a while to appreciate his genius.

The hunting-lodge-turned-palace at Stupinigi left me cold. I found the façade he put on the medieval castle in the centre of the city too heavy. But on the great staircase behind it, and in the Basilica of Superga, the burial place of the royal house, decoration and architectural line are perfectly matched.

Our final delight was to walk through the Galleria Grande of the Venarìa Reale palace, with the sunshine flooding in from the garden on one side and the main courtyard on the other.

Turin is a city of grand arcaded axes, from the river across the Piazza Vittorio Veneto and up the Via Po to the castle, then south down the Via Roma, through the beautiful Piazza San Carlo, to the site of the old Roman Porta Nuova.

It is also the city of the Risorgimento, the liberation movement that in 1861 led to the proclamation of Vittorio Emanuele II, ruler of the House of Savoy, as the first King of Italy. The 150th anniversary of that event will be celebrated next year by the reopening of the Risorgimento museum in the Palazzo Carignano. For those interested in that period, Turin will be the place to visit.

Rita, my Welsh travelling companion, remarked that you needed a holiday after a Martin Randall tour. Given the mass of information and images we had taken in, I could see what she meant. But she obviously soon recovers. The 37th tour will certainly not be her last.

Simon Scott Plummer travelled with Martin Randall Travel (020 8742 3355; www.martinrandall.com) on a seven-day tour costing £1,720. Over the next few months, the company is offering three tours visiting either or both cities: Gastronomic Piedmont from October 4-10, Turin at Christmas from December 21-27, and Genoa and Turin from April 4-10